diff --git a/apps/portal/scripts/dev-prep.mjs b/apps/portal/scripts/dev-prep.mjs
index 37a705fc..d7a42a3c 100644
--- a/apps/portal/scripts/dev-prep.mjs
+++ b/apps/portal/scripts/dev-prep.mjs
@@ -2,7 +2,7 @@
 /* eslint-env node */
 
 // Ensure dev-time Next.js manifests exist to avoid noisy ENOENT errors
-import { mkdirSync, existsSync, writeFileSync } from "fs";
+import { mkdirSync, existsSync, writeFileSync, rmSync } from "fs";
 import { join } from "path";
 import { URL } from "node:url";
 /* global console */
@@ -10,9 +10,28 @@ import { URL } from "node:url";
 const root = new URL("..", import.meta.url).pathname; // apps/portal
 const nextDir = join(root, ".next");
 const routesManifestPath = join(nextDir, "routes-manifest.json");
+const serverDir = join(nextDir, "server");
+const vendorChunksDir = join(serverDir, "vendor-chunks");
+const webpackRuntimePath = join(serverDir, "webpack-runtime.js");
 
 try {
+  // Ensure .next exists
   mkdirSync(nextDir, { recursive: true });
+
+  // Proactively clear stale vendor chunks to avoid version-mismatch runtime errors
+  // e.g. Cannot find module './vendor-chunks/zod@x.y.z.js'
+  try {
+    if (existsSync(vendorChunksDir)) {
+      rmSync(vendorChunksDir, { recursive: true, force: true });
+      console.log("[dev-prep] Cleared .next/server/vendor-chunks");
+    }
+    if (existsSync(webpackRuntimePath)) {
+      rmSync(webpackRuntimePath);
+      console.log("[dev-prep] Removed .next/server/webpack-runtime.js to force regeneration");
+    }
+  } catch (e) {
+    console.warn("[dev-prep] Failed to clear vendor-chunks:", e?.message || e);
+  }
   if (!existsSync(routesManifestPath)) {
     const minimalManifest = {
       version: 5,